The initial National Bladder Cancer Collaborative Group A experience with 4,000 rad adjuvant preoperative radiation therapy followed promptly (within 1 to 28 days) by radical cystectomy and urinary diversion in patients with muscle-invading bladder cancer was monitored prospectively with respect to tolerance of radiation therapy, early postoperative complications and pathologic downstaging. All patients completed the scheduled megavoltage irradiation with, at most, only mild intestinal, urinary or hematologic toxicity. In addition, 86 per cent of the patients completed planned radical cystectomy, with a median interval between radiation therapy and surgery of 13.6 days. No patient died postoperatively. Of the patients 69 per cent recovered with no postoperative complications, while 18 per cent had 1, 9 per cent had 2 and 4 per cent had 3 complications. Pathologic downstaging occurred in 39 per cent of the patients: the disease was downstaged to stage pT0 in 24 per cent and to stage pT1 or pTIS in 15 per cent. Of the patients with an interval of 13 days or less between radiation therapy and surgery the disease was downstaged to stage pT0 in 20 per cent and 63 per cent had no postoperative complications. In patients with an interval of more than 13 days the disease was downstaged in 30 per cent and 76 per cent had no postoperative complications. The results support our rationale for selecting this regimen of adjuvant full dose preoperative radiation therapy, which can shorten the interval between diagnosis and cystectomy, while allowing for the possibility of pathologic downstaging and a radiation dose that is likely to sterilize unresected pelvic micrometastases.